PROJECT SUMMARY/ABSTRACT Osteoarthritis is a highly debilitating disease affecting more than a quarter million people worldwide. Its etiology is multifactorial, with age, gender, obesity, joint injury and heredity among the contributing factors. Articular cartilage is intrinsically unable to heal itself. Any damage results in its progressive loss, inflammation and pain. OA is a disease of the entire joint, and its pathology includes the progressive loss of cartilage, subchondral bone thickening, osteophyte formation, synovial inflammation, degeneration of ligaments and knee menisci, and hypertrophy of the joint capsule. Molecular mechanisms regulating OA are poorly understood. No effective disease-modifying treatments are currently available for OA, leaving pain management or surgical joint replacement as the only therapeutic options. Our preliminary studies identify Ca2+/CaM-dependent kinase kinase 2 (CaMKK2) as a potential therapeutic target against OA. Articular chondrocytes express CaMKK2 and its levels are higher in OA. Genetic ablation or pharmacological inhibition of CaMKK2 protects against cartilage degradation, synovial inflammation, and subchondral bone alterations in a murine model of surgically induced OA. When challenged with interleukin-1?, articular chondrocytes from Camkk2-/- mice display attenuated catabolic and inflammatory responses, in part through downregulation of the adenosine mono-phosphate dependent protein kinase and p38 mitogen activated protein kinase signaling pathways. Based on these data, we hypothesize that CaMKK2 coordinates chondrocyte-responses to injury and inflammatory cytokines, and its function in chondrocytes plays a crucial role in the development of OA. Aim 1 will investigate whether the protection from OA as observed in the global knockout mice comes from the cell-intrinsic role of CaMKK2 in chondrocytes. Aim 2 will elucidate the mechanisms by which CaMKK2 regulates catabolic and inflammatory responses in chondrocytes. Further, absence or inhibition of CaMKK2 suppresses macrophages and osteoclasts. Conditional deletion of CaMKK2 from these cells, as proposed in Aim 3, will provide insights on how CaMKK2 function in synovial macrophages and subchondral bone contribute to OA, and/or influence chondrocyte responses to inflammatory cytokines. Information generated from the proposed studies will provide a basis for developing CaMKK2 inhibition as a novel therapeutic approach to treat OA.